Imatest Glosario Par Pablo Ruiz Garcia Aliasing. Elementos de baja frecuencia, a veces muy molestos, que aparecen cuando la energía de la señal alcanza al sensor digital por encima de la frecuencia Nyquist. El efecto de flecos moire son un tipo de alilasing. Aberración cromática. Es una característica de la lente que provoca que las distintas longitudes de onda formen foco en distintos puntos. Existen dos tipos; longitudinal, donde los diferentes colores forman su foco en planos distintos. Y, lateral, donde la longitud focal de la lente, por lo tanto la ampliación, es diferente para cada color. La aberración cromática […]

Imatest software can measure a great many digital camera image quality factors from test chart images. If you’re just getting started we recommend that you explore the Image Quality factors page. The two most widely used modules, SFRplus and eSFR ISO, can measure a great many image quality factors from single test chart images. Other modules and charts let you work with a wide variety of testing challenges. Running Imatest – Three helpful buttons – RAW files – Misc. controls and utilities ROI Options – Options II – EXIF data – Dropdown menus – Figures – CSV & JSON output    Running Imatest Imatest […]

Setting up and photographing SFR test charts Imatest SFR measures spatial frequency response, also known as the Modulation Transfer Function (MTF), of digital cameras using a slanted-edge (light-to-dark) target, as described in Sharpness: What is it and how is it measured? Although it doesn’t provide the as strong a visual indication of MTF as wedge or sinusoidal chats (such as Log Frequency), it provides a more accurate quantitative measurement and uses space much more efficiently. Old ISO 12233:2000 test chart (left) with Imatest SFR cropping indicated by the red rectangle New ISO 12233:2014 test chart (right– supported with a high […]

Introduction Chromatic aberration (CA) is one of several aberrations that degrade lens performance. (Others include coma, astigmatism, spherical aberration, and curvature of field.) It occurs because the index of refraction of glass varies with the wavelength of light, i.e., glass bends different colors by different amounts. This phenomenon is called dispersion. It appears as color fringing, most visibly on tangential edges near the boundaries of the image. It is sometimes confused with another effect, which we call pixel shift— a color channel offset that is typically uniform over the sensor and can be caused by physical misalignment of multi-chip sensors […]

Photographic scientists and engineers stress the fact that no single number satisfactorily describes the ability of a photographic system to reproduce the small-scale attributes of the subject —Leslie Stroebel,John Compton, Ira Current, Richard Zakia Basic Photographic Materials and Processes, Second edition, p. 273 (Micro-image evaluation chapter), Focal Press, 2000 News: Imatest 2020.1 (March 2020)  Shannon information capacity is now calculated from images of the Siemens star, with much better accuracy than the old slanted-edge measurements, which have been deprecated and replaced with a new method (convenient, but less accurate than the Siemens Star). Siemens Star measurements are the recommended method […]

Introduction – Examples – Oversharpening and Undersharpening  Examples – Unsharp masking (USM) – Links   Introduction to sharpening Sharpening is an important part of digital image processing. It restores some of the sharpness lost in the lens and image sensor. Every digital image benefits from sharpening at some point in its workflow— in the camera, the RAW conversion software, and/or image editor. Sharpening has a bad name with some photographers because it’s overdone in some cameras (mostly low-end compacts and camera phones), resulting in ugly “halo” effects near edges. But it’s entirely beneficial when done properly. Almost every digital camera sharpens images to some degree. Some models […]

Sharpness results derived from Websites Several websites publish images of ISO 12233 test charts that can be entered into Imatest SFR to obtain detailed sharpness measurements. This page contains sharpness results derived from charts downloaded from two sites: Dpreview.com (DPR)   Imaging-resource.com (IR)   The measurements in the tables below come from two areas of the ISO 12233 image, illustrated by red rectangles in the image below. First row: near the center. The rectangle just above the center of the chart (about 15% of the distance to the corners). Second row: near the corner. The rectangle in the lower right […]

Interactive Analysis of Resolution-Related Charts New in Imatest 2020.1 : Shannon information capacity from Siemens Star charts  Introduction – Supported charts – Getting Started – Rescharts Window  –   Rescharts modules Slanted-edge SFR – SFRplus – Log frequency (simple) – Log frequency-contrast – Star – Wedge  Random/Dead Leaves – Focus Score Introduction Imatest™ Rescharts is a highly-interactive interface for running several Imatest modules that can analyze images of several different test charts for resolution-related parameters such as sharpness (i.e., Spatial Frequency Response SFR, which is equivalent to Modulation Transfer Function MTF), color moiré, and fine detail lost to software noise reduction. Several chart types are used for analyzing cameras because most cameras for […]

Overview and introduction to measurements   Summary table— Image quality factors and corresponding test charts and modules Sharpness   Noise   Tonal response & contrast   Color accuracy Lens Distortion   Light Falloff & Nonuniformities   Blemishes   Dynamic range  Lateral Chromatic Aberration   Veiling Glare   Color aliasing and moiré   ISO Sensitivity   Data compression losses   Texture Detail   Information capacity    Software artifacts  Overview and Imatest measurements  Image quality is one of those concepts that’s greater than the sum of its parts. But you can’t ignore the parts if your goal is to produce images of […]

Spanish language translation: Glosario en Espanol Aliasing   Low frequency artifacts, sometimes quite disturbing, that appear when the image sensor receives significant signal energy above the Nyquist frequency. Color aliasing in Bayer sensors can be particularly troublesome. “Moire fringing” is a type of aliasing. See diagram in Nyquist frequency, below. Controlled by means of Anti-Aliasing (Optical Lowpass) Filters, which blur the image slightly (a classic tradeoff).  Aperture   The circular opening at the center of a lens that admits light. Generally specified by the f-stop (f-number), which is the focal length divided by the aperture diameter. A large aperture corresponds […]

Photographing the chart – Running Stepchart – Settings – Output – Temporal noise Auto-exposure – Saving – Dynamic range (DR) – DR definitions – Algorithm   Stepchart measures the tonal response, noise, dynamic range, and ISO sensitivity of digital cameras and scanners using Reflective grayscale step charts such as the Kodak/Tiffen Q-13 and Q-14 Gray Scales, which have a single row of patches (a linear arrangement), or charts such as the ISO-14524 or ISO-15739 charts, with non-linear (multiple rows; may be circular) patch arrangements, shown below, or Transmissive (backlit) grayscale step charts such as the Imatest 36-patch Dynamic Range or 36-patch […]

The SFRplus chart: description and how to photograph it Watch on YouTube. Download 1080p/720p/540p. Purchase SFRplus Test Charts from the Imatest Store. Imatest SFRplus performs highly automated measurements of several key image quality factors using a specially-designed test chart that may be purchased from the Imatest store (recommended) or printed on a high-quality inkjet printer. The user does not need to manually select Regions of Interest (ROIs). Image quality factors include Sharpness, expressed as Spatial Frequency Response (SFR), also known as Modulation Transfer Function (MTF), which can be mapped over the entire image, Noise (limited: eSFR ISO has more detailed […]

Test Charts creates test chart files for printing on high quality inkjet printers. This page focuses on Scalable Vector Graphics (SVG) charts, most of which are used for measuring sharpness (MTF) with Imatest SFR and SFRplus. (Bitmap charts are described elsewhere.) SVG charts can be printed any size at a printer’s maximum quality (i.e., resolution) with no limitations, and they generally require much less storage than bitmap images. The SVG charts designed for automated testing with SFRplus have numerous advantages over the widely-used (pre-2012) ISO 12233 chart. Most of these charts are available through the Imatest Store. We do not […]

In addition to linear step charts (which have a single row of patches), three Imatest modules— Stepchart, Color/Tone Interactive (formerly Multicharts), and Color/Tone Auto (formerly Multitest)— can analyze the tonal response and noise of a number of additional multi-row grayscale charts (reflective and transmissive), most of which are available from the Imatest Store. With most of these charts you can choose between default reference values and a custom reference file that you can measure, or (for 26-patch Dynamic Range charts) are supplied by Imatest. The recommended charts on this page are the 36-patch Dynamic range, ISO-14524, ISO-15739, and 20-patch circular […]

 Analyze the Siemens Star chart News:  Imatest 2020.1 (Feb. 2020)  Shannon information capacity can be calculated from images of the Siemens star, with much better accuracy than slanted-edges. The old slanted-edge method has been deprecated. The new feature will be available in the Pilot program prior to the release.  The white paper, “Camera information capacity: a key performance indicator for Machine Vision and Artificial Intelligence systems“, which briefly introduces information theory, describes the camera information capacity measurement, then shows results (including the effects of artifacts) is now available for download. Imatest 5.0: Half-stars (rotated by multiples of 45º) can now […]

Introduction – Using RAW files – Bayer RAW and RCCC files – dcraw demosaicing – DNG files – Rawview utility – Generalized Read Raw – Decompanding – Creating Synthetic raw images   The unprocessed digital output of an image sensor is called RAW image data. In this document, we sometimes refer to RAW files from commercial cameras or development systems as Camera RAW to distinguish them from Bayer RAW files, which are standard monochrome image files that contain undemosaiced (Bayer) data. Bayer Color Filter Array (CFA)  The pixels in most digital image sensors are covered with the Bayer CFA, which makes […]

Starting with Imatest 3.9, Imatest provides strong support for CPIQ (Camera Phone Image Quality)* Phase 2 measurements. Further detail is available in the CPIQ 2.0 Specifications & Test Methods document. Contact us if you need further information. We are members of CPIQ, and we will will add updated measurements as they become available (expected in early 2016). *CPIQ formerly belonged to I3A (International Imaging Industry Association). It now belongs to the IEEE Standards Association, Working Group P1858. SFR and Acutance For CPIQ, sharpness is measured as Spatial frequency response (SFR) (also called Modulation Transfer Function (MTF)). The SFR, SFRplus ( […]

Introduction to Acutance and SQF   Acutance and Subjective Quality Factor (SQF) are measures of perceived print or display sharpness. SQF was used for years in the photographic industry but has remained unfamiliar to most photographers. Acutance is a relatively new measurement from the IEEE Camera Phone Image Quality (CPIQ) group. Both are metrics which incorporate the effects of The imaging system: The Modulation Transfer Function (MTF) of the camera as a measurement of its intrinsic sharpness. The viewer: The human eye’s sensitivity to each spatial frequency modeled with a Contrast Sensitivity Function (CSF). The viewing conditions: The image display height […]

including raw (image sensor), chroma, and visual noise as well as several types of Dynamic Range calculation News– Imatest 5.2: Multicharts (the highly interactive module for measuring color accuracy, tonal response, and noise) has been renamed to Color/Tone Setup, and Multitest (the fixed/batch-capable version of Multicharts) has been renamed to Color/Tone Auto. For now the old names will be used for INI file sections. An INI File Monitor captures the contents of INI files (which can be used control Imatest IT runs), and displays them in a web browser table.  Imatest 5.1: Color/Tone Setup and Auto can now measure temporal […]

View Release Notes   Index of the Table of Contents Offline documentation Download the website for offline view (with a web browser) Image Quality  IQ factors (KPIs) measured by Imatest, with links to detailed descriptions and instructions. Sharpness  Introductions to sharpness and sharpening; comparisons of different charts; chart quality limitations & how to overcome them Other IQ factors  Noise, SNR, Temporal noise, Dynamic Range (DR),  Chromatic Aberrations, Distortion, Veiling glare, Shannon information capacity, etc. IQ Utilities  Image Processing, SSIM, Image Statistics, Radial geometry  Getting started Why Imatest?, Test charts, Lighting, Image capture technique, Setting up your lab, Using Imatest software […]